Method and System for Enhanced Image Alignment

ABSTRACT

Provided is a method for analyzing image slices. The method includes extracting first and second sub-slices from first and second image slices, respectively, and computing a shift between the first and second image slices based on the first and second sub-slices. The first and second sub-slices overlap. 
     Also provided is a system for analyzing image slices. The system includes an extraction module configured to extract first and second sub-slices from first and second image slices, respectively, and a shift computation module configured to compute a shift between the first and second image slices based on the first and second sub-slices of the extracted sub-slices.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to image slice alignment. More specifically, the present invention relates to the determination of shift information.

2. Related Art

In the field of biometric image analysis, traditional techniques sample an image, such as a fingerprint, as the image is moved or swiped across a sensing mechanism. This sensing mechanism, which could be a fingerprint sensor, captures partial images of the finger during a single swipe. This single swipe produces sets of data at different times and within different coordinate systems. Computer vision technology can then be used to reconstruct an image on the entire fingerprint by sampling these sets of data and combining the partial images to form a complete image of the fingerprint.

The process of transforming these different sets of data into one coordinate system is known to those of skill in the art as image registration. Registration is necessary in order to be able to compare, or integrate, the data obtained from different measurements.

Conventional image registration techniques fall within two realms of classification methods: (i) area-based and (ii) feature-based. The original image is often referred to as the reference image and the image to be mapped onto the reference image is referred to as the target image. For area based image registration methods, the technique looks at the structure of the image via correlation metrics, Fourier properties, and other means of structural analysis.

Techniques used in image registration can be inefficient and slow. Since a relatively large amount of information must be processed, computing shifts between image slices of complex images can be computationally intensive.

What is needed, therefore, are methods and systems that can increase the efficiency and speed of image registration techniques.

SUMMARY OF THE INVENTION

The present invention relates to systems and methods for analyzing image slices. In an embodiment, a method of analyzing image slices includes extracting first and second sub-slices from first and second image slices, respectively, and computing a shift between the first and second image slices based on the first and second sub-slices. The first and second sub-slices overlap.

In another embodiment, a system for analyzing image slices includes an extraction module configured to extract first and second sub-slices from first and second image slices, respectively, and a shift computation module configured to compute a shift between the first and second image slices based on the first and second sub-slices of the extracted sub-slices.

Further embodiments, features, and advantages of the present invention, as well as the structure and operation of the various embodiments of the present invention are described in detail below with reference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable one skilled in the pertinent art to make and use the invention.

FIG. 1 is an illustration of a conventional swipe style biometric sensing device.

FIG. 2 is an illustration of a series of overlapping images of a fingerprint image.

FIGS. 3A and 3B illustrate image slices, according to embodiments of the present invention.

FIGS. 4-6 show fingerprint images, according to embodiments of the present invention.

FIG. 7 is an illustration of a system for analyzing image slices, according to an embodiment of the present invention.

FIG. 8 is an illustration of a shift determining engine, according to an embodiment of the present invention.

FIG. 9 is a flowchart of a method for analyzing image slices, according to embodiments of the present invention.

FIG. 10 is an illustration of a system for analyzing image slices, according to an embodiment of the present invention.

FIG. 11 is a flowchart of a method for analyzing image slices, according to embodiments of the present invention.

FIG. 12 is a block diagram illustration of an exemplary computer system on which the present invention can be implemented.

The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.

DETAILED DESCRIPTION OF THE INVENTION

This specification discloses one or more embodiments that incorporate the features of this invention. The embodiment(s) described, and references in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

FIG. 1 is an illustration of a conventional swipe-style biometric sensing device 100 according to embodiments of the present invention. In FIG. 1, the device 100 includes a sensor 102 for obtaining biometric data (e.g. fingerprint data). In some embodiments, the sensor 102 can be an acoustic impediography or a piezoelectric device. The sensor 102 is used to capture the partial images of a biometric device, such as a finger, discussed above.

FIG. 2 is an illustration of a series of overlapping partial images or image slices 200 of a fingerprint that could be generated from the swipe-style sensor 102 of FIG. 1. By determining shifts between adjacent image slices of image slices 200, image slices 200 can be aligned to form a coherent image.

FIG. 3A shows a first image slice 302 and a second image slice 304, according to embodiments of the present invention. In an embodiment, first slice 302 and second image slice 304 can be image slices of a scanned fingerprint. To form a coherent image of a fingerprint, first and second slices 302 and 304 have to be aligned. As would be appreciated by those skilled in the relevant art(s) based on the description herein, shifts between first and second slices 302 and 304 in the X and Y directions can be used to align first and second slices 302 and 304.

FIG. 3B illustrates first and second slices 302 and 304 when they are properly aligned, according to an embodiment of the present invention. A shift in the Y direction, shown as D_(y) in FIG. 3B, and a shift in the X direction, shown as D_(x) in FIG. 3B, are used to align first and second slices 302 and 304. For example, a shift between first slice 302 and second slice 304 in the X and/or Y direction can be determined by computing a PHAse Transform of first and second slices 302 and 304. For more information regarding the PHAse Transform, please refer to U.S. patent application Ser. No. 12/007,344, filed Jan. 9, 2008 to Jahromi, which is incorporated by reference herein in its entirety. Alternatively, a shift between first slice 302 and second slice 304 in the Y and/or X direction can be determined by computing a correlation between first slice 302 and second slice 304. For more information regarding determining a shift between image slices by computing a correlation, please refer to U.S. Pat. No. 6,459,804, issued Oct. 1, 2002, to Mainguet, which is incorporated by reference herein in its entirety.

As shown in FIG. 3B, first and second slices 302 and 304 overlap in an overlapping region 310. As would be appreciated by those skilled in the relevant art(s) based on the description herein, methods used to compute a shift between image slices typically use information included in a region in which the image slices overlap. For example, methods used to compute a shift between first and second slices 302 and 304 may focus primarily on the information included in overlapping region 310. In an embodiment, information outside of overlapping region 310 may not be as useful in determining a shift between image slices 302 and 304. Furthermore, such information can contribute to an erroneous shift computation and can slow down a shift computation. In embodiments described herein, however, shifts between image slices are computed based on sub-slices extracted from each of the image slices resulting in a faster and/or more accurate shift determination.

As shown in FIG. 3A, first and second slices 302 and 304 include sub-slices 306 and 308, respectively. Sub-slice 306 has dimensions L₁ pixels by H₁ pixels. Sub-slice 308 has dimensions L₂ pixels by H₂ pixels. First and second slices 302 and 304 both have dimensions L pixels by H pixels. In an embodiment, L, L₁, and L₂ can refer to the length of the image slice or sub-slice (i.e., the dimension of the slice or sub-slice in the X direction). Similarly, H, H₁, and H₂ can refer to the height of the image slice or sub-slice (i.e., the dimension of the slice or sub-slice in the Y direction). The length of sub-slices 306 and 308 can range from one pixel up the length of first and second slices 302 and 304, respectively (e.g., L pixels). Similarly, the height of sub-slices 306 and 308 can range from one pixel up to the height of first and second slices 302 and 304, respectively (e.g., H pixels). In the embodiment of FIGS. 3A and 3B, first and second slices 302 and 304 are shown to have identical lengths and heights. However, in alternative embodiments, first and second slices 302 and 304 can have different lengths and/or heights.

In an embodiment, shifts in the X and Y directions between first and second slices 302 and 304 are determined based on sub-slices 306 and 308. In such an embodiment, the shift computation methods described above, or other methods known to those skilled in the relevant art(s), are applied to sub-slices 306 and 308 instead of first and second slices 302 and 304. Thus, sub-slices 306 and 308 are effectively treated as the slices between which the shifts are computed.

As described above, the information contained in overlapping region 310 can be significant in determining shifts between first and second slices 302 and 304. The lengths, heights, and placement of sub-slices 306 and 308 with respect to first and second slices 302 and 304, respectively, are determined so that sub-slices 306 and 308 substantially overlap overlapping region 310. Thus, when sub-slices 306 and 308 are extracted from first and second slices 302 and 304, respectively, a substantial portion of overlapping region 310 is contained in an overlapping region 312 in which sub-slices 306 and 308 overlap. In such a manner, less important information to a shift computation, e.g., information outside of overlapping region 310 is ignored, while information that is useful to the determination of a shift, e.g., overlapping region 310, is used in the shift computation.

The dimensions (e.g., lengths and widths) and the placement of sub-slices 306 and 308 with respect to first and second slices 302 and 304, respectively, can influence the accuracy with which shifts between images slices 302 and 304 are determined. In an embodiment, as the portion of overlapping region 310 overlapped by sub-slices 306 and 308 increases and the portion of first and second slices 302 and 304 outside of overlapping region 310 overlapped by sub-slice 306 and/or sub-slice 308 decreases, the accuracy and speed of a shift computation according to sub-slices 306 and 308 increases.

As shown in FIG. 3B, each of sub-slices 306 and 308 substantially overlap overlapping region 310. For example, both sub-slices 306 and 308 substantially overlap overlapping region 310 in the Y direction. Sub-slices 306 and 308 also overlap a substantial portion of overlapping region 310 in the X direction. In the embodiment in which first and second slices 302 and 304 are image slices of a fingerprint scan, capturing the extent of overlapping region 310 in the Y direction may be more important than capturing the extent of overlapping region 310 in the X direction. For example, it may be known that the finger being scanned will move mostly in the Y direction relative to the scanner. Furthermore, the sensor, and thus the image slices it produces, may have a length that is substantially larger than its height. Thus, it can be determined that a shift in the X direction will be substantially smaller than the length of first and second slices 302 and 304 and that the shift in the Y direction will be comparable to the height of first and second slices 302 and 304. Therefore, only a portion of overlapping region 310 in the X direction and as much as possible of overlapping region 310 in the Y direction may be used to accurately compute shift information.

If the shifts between first and second slices 302 and 304 are known before sub-slices 306 and 308, respectively, are extracted, the dimensions of sub-slices 306 and 308 can be determined so that desired portions of overlapping region 310 are captured. For example, in the embodiment in which image slices 302 and 304 have a height of 16 pixels (e.g., H=16) and the shift in the Y direction is known to be 6 pixels, the heights of sub-slices 306 and 308 can be 10 pixels (e.g., H₁=H₂=16−6=10). In such a manner, both sub-slices 306 and 308 can completely overlap in region 310 in the Y direction yet contain no extra information in the Y direction, e.g., outside of overlapping region 310. More generally, the height of a sub-slice extracted from an image slice may be determined as the shift in the Y direction between the respective image slice and another image slice (e.g., an adjacent image slice with which the respective image slice will be aligned) subtracted from the height of the respective image slice.

However, as will be apparent to those skilled in the relevant art(s) based on the description herein, it is typically difficult to know a shift between first and second slices 302 and 304 before sub-slices 306 and 308 are extracted. In such an embodiment, the dimensions of sub-slices 306 and 308 may be determined based on the expected shift between image slices 302 and 304. For example, if it is determined that the expected shift in the Y direction between first and second slices 302 and 304 is 6 pixels and the height of first and second slices 302 and 304 is 16 pixels, the height of sub-slices 306 and 308 may be determined to be 10 pixels.

In an embodiment, the lengths of sub-slice 306 and 308 may be determined based on an expected shift between first and second slice 302 and 304 in the X direction in a substantially similar manner.

In another embodiment, the lengths of sub-slices 306 and 308 can be determined based on a known range of typical shifts in the X direction, so that sub-slices 306 and 308 are completely included in overlapping region 310 in the X direction. For example, it may be known that a shift in the X direction will not exceed 5 pixels. In an embodiment in which the length of image slices 302 and 304 is 120 pixels (e.g., L=120), the length of sub-slices 306 and 308 may be selected to be less than or equal to 115 pixels (120−5=115), e.g., 64 pixels. In contrast to the heights of sub-slices 306 and 308, which are determined to include as much of the height of overlapping region 310 as possible, the lengths of sub-slices 306 and 308 can be determined so that sub-slices 306 and 308 are completely included in overlapping region 310, since, as described above, the shift in the X direction between first and second slices 302 and 304 is much smaller than the length of first and second slices 302 and 304 and a finger in a fingerprint scan may move predominantly and predictably in the Y direction.

In addition to the dimensions, the locations of first and second slices 302 and 304 from which sub-slices 306 and 308, respectively, are extracted are also important in accurately and quickly computing shifts between first and second slices 302 and 304. As shown in FIG. 3A, sub-slices 306 and 308 are non-symmetric. In other words, sub-slices 306 and 308 do not occupy the same region of their respective image slices. In an embodiment, sub-slices 306 and 308 may be non-symmetric so that they can maximize their overlap with overlapping region 310. For example, it may be known before the extraction of sub-slices 306 and 308 that overlapping region 310 will include a portion of the bottom edge of first slice 302 and a portion of the top edge of second slice 304, e.g., since first slice 302 is received from a sensor before second slice 304 and the finger is known to be moving downward in the Y direction relative to sensor. Thus, sub-slice 306 can be located such that its bottom edge coincides with the bottom edge of first slice 302 and sub-slice 308 can be located such that its top edge coincides with a top edge of second slice 304.

In another embodiment, the locations in the X direction from which sub-slices 306 and 308 are extracted can be determined in a similar fashion, e.g., instead of top and bottom edges, left and right edges. However, in an alternate embodiment, the direction of the shift (e.g., the mathematical sign) may not be known in X direction before sub-slices 306 and 308 are extracted. For example, a finger may move unpredictably in the X direction during a swipe. Thus, sub-slices 306 and 308 can be extracted from a central location of first and second slices, respectively, in an attempt to ensure they at least partially overlap overlapping region 310. In an embodiment, a non-symmetric pair of sub-slices can be non-symmetric with respect to the X direction, the Y direction, or both.

Thus, as described above, the locations from which sub-slices are extracted may be non-symmetric and may be determined before the sub-slices are extracted from their respective image slice partially based on whether the respective slice will overlap with the other image slice in a bottom, top, left, right, or an unpredictable region. However, shifts between image slices are typically not known before the sub-slices are extracted. Thus, the dimensions of the sub-slices are determined based on an expected shift or a range of expected shifts between the respective image slices.

FIGS. 4-6 show fingerprint images that include image slices aligned using sub-slices of different heights, according to an embodiment of the present invention. The image slices aligned to form the fingerprint images are 8 pixels in height and 192 pixels in length. The extracted sub-slices are non-symmetric with respect to the Y direction with sub-slices either sharing an edge with a top edge of an image slice or a bottom edge of its respective image slice based on where the respective image slice is expected to overlap with the next image slice, as described above. The sub-slices are located in a central portion of the respective image slices with respect to the X direction.

FIG. 4 shows fingerprint images 402-414. Fingerprint images 402, 404, 406, 408, 410, 412, and 414 are aligned using shifts determined using sub-slices that are 2, 3, 4, 5, 6, 7, and 8 pixels in height, respectively. In FIG. 4, each of the image slices used to form images 402-414 have a shift of 5 pixels with adjacent image slices. Thus, as described above, a fingerprint image that is aligned with sub-slices that have a height of 3 pixels, e.g., 8−5=3, would produce the most accurate fingerprint image. As shown in FIG. 4, fingerprint image 404 that includes image slices aligned using sub-slices that have a height of 3 pixels is the most accurate fingerprint image out of fingerprint images 402-414.

FIG. 5 shows fingerprint images 502 through 514 that include image slices aligned using sub-slices of different height. In particular, fingerprint images 502, 504, 506, 508, 510, 512, and 514 are aligned include image slices that are aligned using shifts determined using sub-slices that have a height of 2, 3, 4, 5, 6, 7. and 8 pixels in height, respectively. Image slices used to form fingerprint images 502-514 are known to have a shift in the Y direction of 2 pixels with adjacent image slices. Image slices that are known to have a shift in the Y direction of 2 pixels should be best aligned based on shifts determined using sub-slices that have a height of 6, e.g., 8−2=6, pixels. As shown in FIG. 5, fingerprint image 510, aligned using shifts determined based on sub-slices that have a height of 6 pixels, is the most accurate fingerprint image out of fingerprint images 502-514 shown in FIG. 5.

FIG. 6 shows fingerprint images 602 through 614 aligned using shifts determined using sub-slices of different height. In particular, fingerprint images 602, 604, 606, 608, 610, 612, and 614 include image slices that are aligned shifts determined using sub-slices of height 2, 3, 4, 5, 6, 7, and 8 pixels in height. Image slices used to form fingerprint images 602-614 are known to have a shift in the Y direction of 6 pixels with adjacent image slices. Thus, a fingerprint image that includes image slices aligned using shifts determined using sub-slices that have a height of 2 pixels, e.g., 8−6=2, would be expected to produce the most accurate fingerprint image. As shown in FIG. 6, fingerprint image 602 is the most accurate fingerprint image out of the fingerprint images 602-614.

Thus, if the shift between a pair of image slices can be estimated, the dimensions of the sub-slices can be determined so that the shift between the image slices can accurately be determined. Further, as shown in FIGS. 4-6, images including image slices aligned using shifts determined using sub-slices that have heights close to the optimal heights also produce relatively accurate images. Thus, even in the case that the expected shift is not precisely correct, accurate shift information may be obtained and image slices can be accurately aligned. For example, images 402, 406, and 408 of FIG. 4, images 508, 512, and 514 of FIG. 5, and images 604 and 606 of FIG. 6 are not aligned using shifts determined using the best height for the shifts in the Y direction for each of the respective sets of image slices, but still may be generally accurate fingerprint images.

FIG. 7 shows a system 700 for processing image slices, according to an embodiment of the present invention. System 700 includes a sensor 702 and a shift determining module 704. Sensor 702 is configured to output image slices. For example, sensor 702 can be a swipe fingerprint scanner. In alternate embodiments, sensor 702 can be other types of sensors that produce image slices, e.g., a retinal scanner.

Shift determining module 704 includes shift determining engines 706 a-706 g, collectively referred to as shift determining engines 706 and a control module 708. FIG. 8 shows a shift determining engine 800, according to an embodiment of the present invention. One or more of shift determining engines 706 can be implemented as shift determining engine 800, shown in FIG. 8. Shift determining engines 706 as well as control module 708 may be implemented as hardware, software, firmware, or any combination thereof. The operation of system 700 will be described with reference to FIG. 9, below.

FIG. 9 shows a flowchart 900 of a method for analyzing image slices, according to an embodiment of the present invention. Flowchart 900 is described with reference to the embodiments of FIGS. 7 and 8. However flowchart 900 is not limited to those embodiments. The steps shown in FIG. 9 do not necessarily have to occur in the order shown. The steps of FIG. 9 are described in detail below.

Flowchart 900 begins with step 902. In step 902, a sub-slice is extracted from each image slice of a pair of image slices. For example, in FIG. 7, each engine of shift determining engines 706 receives a pair of image slices from sensor 702 and extracts a sub-slice from each image slice of the pair of received image slices.

For example, as described above, shift determining engines 706 may be implemented as shift determining engine 800 shown in FIG. 8. Extraction module 802 of shift determining engine 800 may receive the pair of image slices and extract a sub-slice from each of the pair of sub-slices.

In an embodiment, each of shift determining engines 706 extracts sub-slices that have different dimensions (e.g., according to different expected shifts). For example, in the embodiment in which sensor 702 outputs image slices that have a height of 8 pixels shift determining engines 706 a, 706 b, 706 c, 706 d, 706 e, 706 f, and 706 g can extract sub-slices with height of 2, 3, 4, 5, 6, 7, and 8 pixels, respectively, corresponding to expected shifts of 6, 5, 4, 3, 2, 1, and 0 pixels, respectively.

Furthermore, each of shift determining engines 706 can extract sub-slices with the same length. The length of the sub-slices can be determined based on a range of typical shifts in the X direction, as described above with reference to the lengths of sub-slices 306 and 308.

The sub-slices extracted by each of shift determining engines 706 may also be non-symmetric. For example, the extracted sub-slices may be non-symmetric in the Y direction and symmetric in the X direction. In particular, the sub-slices can share an edge with a top or bottom edge of a respective image slice depending on where the image slice will overlap with the other image slice of the pair of received image slices and can be located in a central portion of the respective image slice with respect to the X direction, as described above with respect to sub-slices 306 and 308.

In step 904, shifts between the pair of image slices are computed based on the extracted sub-slices. For example, shifts may be computed by computing a PHAse Transform of or a correlation between the extracted sub-slices, as described above. A shift may be computed in each of the X and Y directions.

For example, in FIG. 7, shift determining engines 706 compute a shift between the received pair image slices using extracted sub-slices. For example, in the embodiment in which shift determining engines 706 are implemented as shift determining engine 800 shown in FIG. 8, shift computation module 804 receives the extracted sub-slices from extraction module 802 and computes a shift by computing a PHAse Transform of the extracted slices. As described above, each of shift determining engines 706 can extract sub-slices with different dimensions. Thus, in step 904, shifts can be computed between the pair of image slices based on sub-slices extracted with different dimensions (e.g., different heights).

In step 906, a shift is determined based on the computed shifts. The determined shift may be used to align the pair of image slices. For example, a median or mean of a set of computed shifts may be calculated to determine the shift. In alternate embodiments, other statistical operators know to those skilled in the relevant art(s) can be used to determine a shift from the computed shifts. In a further embodiment, a shift is determined in both the X and Y directions in such a manner.

For example, in FIG. 7, control module 708 receives computed shifts from shift determining engines 706. Control module 708 computes a mean or median of the received computed shifts to determine shifts that are used to align the received pair of image slices. In the embodiment in which control module 708 computes a mean, the mean may be a decimal number. In such an embodiment, the decimal number may be rounded to an integer so that the two image slices can be aligned. In a further embodiment, control module 708 receives a first set of shifts in the X direction and a second set of shifts in the Y direction and determines shifts in the X and Y to be used to align the pair image slices in the manner described above.

In step 908, an optimal dimension is identified. For example, the optimal dimension may be an optimal height of a sub-slice. For example, in FIG. 7, control module 708 may identify an optimal height of a sub-slice. The optimal height may correspond to a shift determining engine of shift determining engines 706 that outputs the shifts determined in step 906. For example, based on the received computed shifts, control module 708 may determine shifts that match the shifts computed by shift determining engine 706 a. Control module 708 may then identify shift determining engine 706 a as outputting accurate computed shifts. Thus, control module 708 determines that the height of the sub-slices extracted by shift determining engine 706 a, e.g., two pixels in height, is the optimal dimension.

In step 910, it is determined whether the optimal dimension is reliable. For example, it may be determined whether sub-slices having the optimum dimension can be used to accurately determine a shift between another pair of image slices. For example, in FIG. 7, control module 708 may determine whether shifts computed by shift determining engine 706 a will be accurate for a subsequent pair of image slices. For example, control module 708 may make such a determination by determining whether the computed shift outputted by shift determining engine 706 a has been equal to the shift determined by control module 708 for a predetermined number of pairs of slices.

If it is determined that a reliable optimal dimension has not been determined, flowchart 900 returns to step 902. Alternatively, if an optimum dimension has been determined, flowchart 900 proceeds to step 912.

In step 912, sub-slices are extracted from another pair of image slices. The extracted sub-slices have the optimal dimension. For example, in FIG. 7, control module 708 may disable shift determine engines 706 b-706 g if it is determined that the height of sub-slices extracted by shift determining engines 706 a is a reliable optimal dimension. In such an embodiment, the shift outputted by control module 708 is identical to the shift computed by shift determining engine 706 a. By disabling shift determining engines 706 b-706 g power may be saved and the shift computation may be made faster.

In step 914, a shift is computed based on the extracted sub-slices. In an embodiment, step 914 is substantially similar to step 904. However in step 914, the shift is computed based on extracted only sub-slices that have the optimum dimension. For example, in FIG. 7, shift determining engine 706 a computes a shift between two image slices based on sub-slices that have the optimal dimension.

After step 914, flowchart 900 returns to step 910. Thus, it is determined again whether the optimum dimension is still reliable. If the optimum dimension is determined to be still reliable, shifts between image slices can still be determined based on sub-slices that have the optimum dimension. If not, a set of shifts are computed based on sub-slices that have varying dimensions and a shift is determined from the set of shifts, as described above.

As shown in FIG. 9, flowchart 900 may return to step 902 after the completion of step 906. In such an embodiment, a shift can continually be determined from a set of computed shifts, each of which is computed based on extracted sub-slices that have a different dimension (e.g., a different height). For example, in FIG. 7, each of shift determining engines 706 continually computes shifts using sub-slices of different dimensions. Alternatively, prior data can be used so that one or more of shift determining engines 706 can be turned off or otherwise disabled to save power and computing time (e.g., through the identification of an optimal dimension). In such an embodiment, control module 708 effectively determines an expected shift, e.g., a height of a sub-slice which is a function of the expected shift, as described above, and determines a shift based on sub-slices having a height corresponding to the expected shift. As long as the expected shift remains reliable, control module 708 can keep one or more of shift determining engines 706 turned off or otherwise disabled.

FIG. 10 shows a system for processing image slices 1000, according to an embodiment of the present invention. System 100 includes a sensor 1002 and a shift determining module 1004. Sensor 1002 may be substantially similar to sensor 702 described above. Shift determining module 1004 includes a shift determining engine 1006 and a control module 1008. Shift determining engine 1006 includes an extraction module 1010 and a shift computation module 1012. The operation of system 1000 will be described with reference to FIG. 11 below.

FIG. 11 shows a flowchart 1100 of a method for analyzing image slices, according to an embodiment of the present invention. Flowchart 1100 is described with reference to the embodiment of FIG. 10. However flowchart 1100 is not limited to that embodiment. The steps shown in FIG. 11 do not necessarily have to occur in the order shown. The steps of FIG. 11 are described in detail below.

In step 1102, a sub-slice is extracted from each of a first and second image slice. The dimension of the extracted sub-slices may be based on an initial expected shift and/or a range of expected shifts. The initial expected shift may be determined based on prior information (e.g., prior information regarding initial image slices produced in a scan of a fingerprint).

For example, in FIG. 10, extraction module 1010 of shift determining engine 1006 receives first and second image slices from sensor 1002. Extraction module 1010 also receives an initial shift from control module 1008. Based on the initial expected shift in the Y direction received from control module 1008, extraction module 1010 determines the heights of the sub-slices. Alternatively, the initial expected shift may be programmed into extraction module 1010.

For example, extraction module 1010 can determine the heights of the subs-slices as being the initial expected shift in the Y direction subtracted from the heights of the first and second image slices. The length of the sub-slices may be determined based on a range of expected shifts in the X direction received from control module 1008 or programmed in extraction module 1010, as described with respect to sub-slices 306 and 308. The location of the sub-slices with respect to the first and second image slices can be determined in a manner similar to as described with respect to step 902 of flowchart 900.

In step 1104, a shift is computed between the first and the second image slices based on the extracted sub-slices. The shift between the first and second image slices may be computed by computing a PHAse Transform of or a correlation between the extracted sub-slices, as described above.

For example, in FIG. 10, shift computation module 1012 computes a shift between the first and second image slices based on the extracted sub-slices slices. Shift computation module 1010 may compute shifts by computing a PHAse Transform of the extracted sub-slices.

In step 1106, it is determined whether sufficient data has been received so that an expected shift can be determined. In an embodiment, an expected shift may be determined on past shift information. For example, in FIG. 10, control module 1008 may require 3 past shifts before an expected shift can be determined. Thus, if control module 1008 has not received at least 3 shifts, an expected shift cannot be determined by control module 1008.

If sufficient data has not been received to determine an expected shift, flowchart 1100 returns to step 1102. In an embodiment, steps 1102 through 1106 are repeated until sufficient data is received to determine an expected shift. Once sufficient data has been received to determine an expected shift, flowchart 1100 proceeds to step 1108. In step 1108, an expected shift is determined. For example, the expected shift may be determined as a mean or median of a past set of values. For example, in FIG. 10, control module 1008 may compute a median of the last 3 shifts outputted by shift computation module 1012 to determine an expected shift. In alternate embodiments, control module 1008 may use other statistical operators to compute an expected shift. For example, control module 1008 may compute an average of the last 3 shifts outputted by shift computation module 1012 to compute the expected shift. Expected shifts in the X and/or Y directions may thus be determined based on past shift information.

In step 1110, a sub-slice is extracted from each of a third and fourth image slices. In an embodiment, step 1110 is substantially similar to step 1102 described above. However in step 1110, one or more dimensions of the sub-slices are determined based on the expected shift rather than an initial expected shift. For example, in FIG. 10, extraction module 1010 extracts sub-slices from third and fourth image slices based on the expected shift computed buy control module 1008. In particular, the height of the sub-slices extracted from the third and fourth image slices may be determined based on the expected shift in a manner similar to as described with reference sub-slices 306 and 308, above. The length and locations of the sub-slices with respect to the first and second image slices can be similar to as described with reference to step 1102, above.

In step 1112 a shift is computed between the third and fourth image slices based on the extracted sub-slices. In an embodiment, step 1112 is substantially similar to step 1104, however the sub-slices used in step 1112 have one or more dimensions determined by an expected shift rather than an initial expected shift.

As shown in FIG. 11, flowchart 1100 returns to step 1108 after step 1112. Thus, once sufficient data is received to determined an expected shift, one or more dimensions of the extracted sub-slices is determined based on the determined expected shift rather than the initial expected shift.

FIGS. 7 and 10 show systems 700 and 1000 for processing image slices according to an embodiment of the present invention. In system 700, multiple shift determining engines are run in parallel and a shift is selected from the shift determining engines to be used to align image slices. System 700 can have one or more shift determining engines turned off or otherwise disabled if it is determined that one of the shift determining engines can provide accurate shift information.

System 1000 utilizes a feedback loop that allows the dimensions of the sub-slices to be adjusted in real time based on previous shift information. Since system 1000 only has a single shift determining engine running at a single time, system 1000 may be more efficient with respect to power use and speed than system 700. Furthermore, in the embodiment in which shift determining engines are implemented as hardware, the embodiment of system 1000 may require less space to implement than the embodiment of system 700. As described above, statistical operators used to determine an expected shift compute the expected shift based on past shift information. The number of shifts considered in determining the expected shift may be changed based on memory availability in a system. For example, if a system has a large amount of available memory, a determination of the expected shift may include more shift values.

The present invention (i.e., elements of FIGS. 7, 8 and 10 and flowcharts 900 and 1100 or any part(s) or function(s) thereof) may be implemented using hardware, software or a combination thereof and may be implemented in one or more computer systems or other processing systems. However, the manipulations performed by the present invention were often referred to in terms, such as adding or comparing, which are commonly associated with mental operations performed by a human operator. No such capability of a human operator is necessary, or desirable in most cases, in any of the operations described herein which form part of the present invention. Rather, the operations are machine operations. Useful machines for performing the operation of the present invention include general purpose digital computers or similar devices.

In fact, in one embodiment, the invention is directed toward one or more computer systems capable of carrying out the functionality described herein. An example of a computer system 1200 is shown in FIG. 12.

The computer system 1200 includes one or more processors, such as processor 1204. The processor 1204 is connected to a communication infrastructure 1206 (e.g., a communications bus, cross over bar, or network). Various software embodiments are described in terms of this exemplary computer system. After reading this description, it will become apparent to a person skilled in the relevant art(s) how to implement the invention using other computer systems and/or architectures.

Computer system 1200 can include a display interface 1202 that forwards graphics, text, and other data from the communication infrastructure 1206 (or from a frame buffer not shown) for display on the display unit 1230.

Computer system 1200 also includes a main memory 1208, preferably random access memory (RAM), and may also include a secondary memory 1210. The secondary memory 1210 may include, for example, a hard disk drive 1212 and/or a removable storage drive 1214, representing a floppy disk drive, a magnetic tape drive, an optical disk drive, etc. The removable storage drive 1214 reads from and/or writes to a removable storage unit 1218 in a well known manner. Removable storage unit 1218 represents a floppy disk, magnetic tape, optical disk, etc. which is read by and written to by removable storage drive 1214. As will be appreciated, the removable storage unit 1218 includes a computer usable storage medium having stored therein computer software and/or data.

In alternative embodiments, secondary memory 1210 may include other similar devices for allowing computer programs or other instructions to be loaded into computer system 1200. Such devices may include, for example, a removable storage unit 1222 and an interface 1220. Examples of such may include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an erasable programmable read only memory (EPROM), or programmable read only memory (PROM)) and associated socket, and other removable storage units 1222 and interfaces 1220, which allow software and data to be transferred from the removable storage unit 1222 to computer system 1200.

Computer system 1200 may also include a communications interface 1224. Communications interface 1224 allows software and data to be transferred between computer system 1200 and external devices. Examples of communications interface 1224 may include a modem, a network interface (such as an Ethernet card), a communications port, a Personal Computer Memory Card International Association (PCMCIA) slot and card, etc. Software and data transferred via communications interface 1224 are in the form of signals 1228 which may be electronic, electromagnetic, optical or other signals capable of being received by communications interface 1224. These signals 1228 are provided to communications interface 1224 via a communications path (e.g., channel) 1226. This channel 1226 carries signals 1228 and may be implemented using wire or cable, fiber optics, a telephone line, a cellular link, a radio frequency (RF) link and other communications channels.

In this document, the terms “computer program medium” and “computer usable medium” are used to generally refer to media such as removable storage drive 1214 and a hard disk installed in hard disk drive 1212. These computer program products provide software to computer system 1200. The invention is directed to such computer program products.

Computer programs (also referred to as computer control logic) are stored in main memory 1208 and/or secondary memory 1210. Computer programs may also be received via communications interface 1224. Such computer programs, when executed, enable the computer system 1200 to perform the features of the present invention, as discussed herein. In particular, the computer programs, when executed, enable the processor 1204 to perform the features of the present invention. Accordingly, such computer programs represent controllers of the computer system 1200.

In an embodiment where the invention is implemented using software, the software may be stored in a computer program product and loaded into computer system 1200 using removable storage drive 1214, hard drive 1212 or communications interface 1224. The control logic (software), when executed by the processor 1204, causes the processor 1204 to perform the functions of the invention as described herein.

In another embodiment, the invention is implemented primarily in hardware using, for example, hardware components such as application specific integrated circuits (ASICs). Implementation of the hardware state machine so as to perform the functions described herein will be apparent to persons skilled in the relevant art(s).

In yet another embodiment, the invention is implemented using a combination of both hardware and software.

CONCLUSION

Example embodiments of the methods, systems, and components of the present invention have been described herein. As noted elsewhere, these example embodiments have been described for illustrative purposes only, and are not limiting. Other embodiments are possible and are covered by the invention. Such other embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. Thus, the breadth and scope of the present invention should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.

The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. 

1. A method for analyzing image slices, comprising: 1) extracting first and second sub-slices from first and second image slices, respectively, wherein the first and second sub-slices overlap; and 2) computing a shift between the first and second image slices based on the first and second sub-slices.
 2. The method of claim 1, further comprising: 3) extracting third and fourth sub-slices from the first and second image slices, respectively, wherein the third and fourth sub-slices overlap, wherein the third and fourth sub-slices each have a dimension different from a dimension of the first sub-slice; 4) computing a second shift between the first and second image slices based on the third and fourth sub-slices; and 5) determining a third shift between the first and second image slices based at least on the first and second shifts, wherein the third shift is used to align the first and second image slices.
 3. The method of claim 2, further comprising: 6) identifying an optimal dimension, wherein third shift is equal to the second shift, wherein the dimension of the third sub-slice and the dimension of the fourth sub-slice match the optimal dimension; 7) extracting first and second sub-slices from third and fourth image slices, respectively, the first and second sub-slices of the third and fourth image slices each having a dimension that matches the optimal dimension; and 8) computing a shift between the third and fourth image slices based on the first and second sub-slices of the third and fourth image slices, respectively.
 4. The method of claim 1, further comprising: 3) computing a shift between each pair of image slices of a plurality of pairs of image slices; 4) determining an expected shift based on the shifts computed in step (3); and 5) determining an optimal dimension based on the expected shift; wherein each of the first and second sub-slices have a dimension that matches the optimal dimension.
 5. The method of claim 4, wherein step (4) comprises: computing a mean or median of the shifts.
 6. The method of claim 1, wherein step (2) comprises: computing a PHAse Transform of the first and second sub-slices.
 7. The method of claim 1, wherein step (2) comprises: computing a correlation between the first and second sub-slices.
 8. The method of claim 1, further comprising: 3) aligning the first and second slices based on the computed shift.
 9. The method of claim 1, wherein the first and second sub-slices are non-symmetric.
 10. A system for analyzing image slices, comprising: an extraction module configured to extract first and second sub-slices from first and second image slices, respectively; and a shift computation module configured to compute a shift between the first and second image slices based on the first and second sub-slices.
 11. The system of claim 10, further comprising: an alignment module configured to align the first and second image slices based on the shift computed by the shift computation module.
 12. The system of claim 10, further comprising: a second extraction module configured to extract third and fourth sub-slices from the first and second image slices, respectively, wherein the third and fourth sub-slices overlap, wherein the third and fourth sub-slices each have a dimension different from a dimension of the first sub-slice; a second shift computation module configured to compute a second shift between the first and second image slices based on the third and fourth sub-slices; and a control module configured to determine a third shift between the first and second image slices based at least on the first and second shifts, wherein the third shift is used to align the first and second image slices.
 13. The system of claim 10, wherein: the shift determining module is configured to receive third and fourth sub-slices from the first and second image slices, respectively, wherein the third and fourth sub-slices overlap, wherein the third and fourth sub-slices each have a dimension different from a dimension of the first sub-slice and compute a second shift between the first and second image slices based on the third and fourth sub-slices; further comprising: a control module configured to determine a third shift between the first and second image slices based at least on the first and second shifts, wherein the third shift is used to align the first and second image slices.
 14. The system of claim 10, further comprising: a control module configured to determine an expected shift based a plurality of received shifts; wherein the extraction module is configured to determine a dimension of the first sub-slice and a dimension of the second sub-slice based at least on the expected shift.
 15. The system of claim 10, wherein the shift computation module is configured to determine a shift between the first and second image slices by computing a PHAse Transform of the first and second sub-slices.
 16. The system of claim 10, wherein the shift computation module is configured to determine a shift between first and second image slices by computing a correlation technique between first and second sub-slices. 